Field of the Invention
The present invention relates to an in-cell touch type display device, and more particularly, to an in-cell touch type display device with improved touch performance.
Discussion of the Related Art
Facing information society, display field of displaying electric information signals has been rapidly advanced, and accordingly, various flat display devices have been developed and used. As flat display devices, a liquid crystal display device (LCD), a plasma display panel device (PDP), an organic light emitting diode (OLED) display device and the like are used.
Among the flat display devices, LCDs are widely used because they have advantages of small size, light weight, thin profile, low power consumption, and the like.
Recently, an LCD having a gate-in panel (GIP) structure in which a gate driving circuit is directly formed in an array substrate of a liquid crystal panel is widely used.
Further, a touch function has been added to an LCD. Particularly, to achieve thin profile, an in-cell touch type LCD, in which a touch screen is embedded, is used.
In the in-cell touch type LCD, touch blocks arranged in a matrix form in a display region are defined, self-capacitance type touch electrodes are arranged corresponding to respective touch blocks, and sensing lines are connected to respective touch electrodes. In this configured LCD, a display period and a touch sensing period alternate, and during the touch sensing period, a touch driving signal for a touch sensing is outputted to each touch sensing line and is applied to the corresponding touch electrode.
In such a in-cell touch type LCD according to the related art, since the sensing line overlaps a signal line such as a gate line or data line, a coupling capacitance is produced and a capacitive load is produced.
Because of this capacitive load, an RC (resistance-capacitance) delay is caused. Accordingly, a touch sensitivity is reduced, and a touch performance is reduced.
FIG. 1 is an equivalent circuit diagram of an in-cell touch type LCD according to the related art.
Referring to FIG. 1, resistive loads Lr1 and Lr2 generally exist at a sensing line SL and a signal line SGL, respectively, and a capacitive load Lc exists between the sensing line SL and the signal line SGL. In a touch sensing period, a touch driving signal Vt in a pulse waveform is applied to the sensing line SL, a low voltage Vs in a DC form is continuously applied.
Accordingly, a voltage difference as shown in the waveform of the touch driving signal Vt is produced between both ends of the capacitive load Lc, and thus a signal current It flowing on the sensing line SL inflows into the capacitive load Lc. Thus, the touch driving signal Vt has an RC delay and a pulse waveform is distorted, and thus a touch performance may be reduced.
This problem happens with various types of display devices, including an OLED display device, that use an in-cell touch configuration.